Excitation control system for vapor electric devices



Aug. 24, 194s.

`J. H. COX EXCITATION CONTROL SYSTEM FOR VAPOR -ELECTRIC DEVICES Filed May 27, 1943 2 Sheevts-Sheet 1 QIil lNvENoR Josep/ H (0I.

mJy/4 ATroRNEY Aug. 24, 1948. J. H. cox 2,4475638 EXCITATION CONTROL SYSTEM FR VAPOR ELECTRIC DEVICES Filed May 27, 1943 2 Sheets-Sheet 2 wlTNEss: y I NVENTOR ct N- Jbse/o/ZH (01.

ATTORNEY Patented Aug. Z4, 1948 EXCITATION CONTROL SYSTEM FORv varon ELECTRIC DEvIoEs Joseph H. Cox; Forest Hills, Pa., assignor to Westinghouse Electric Corporation,'East Pittsburgh, Pa., a corporation of Pennsylvania Application May 27, 1943, serial No. 488,637

My invention relates to a vapor-electric device and particularly to an excitationcontroll `system for such devices. i

In the operation of vapor-electric devices of the make-alive type, particularly when excitedV line voltage, such as caused by a line fault, thel various units cease operating in a ragged manner so that the last units to stop are overloaded and their breakers trip out because of their overload. When the line voltage is restored and excitation is resumed, the rectiiiers remaining on the bus will loe-overloaded, and, consequently, their breakers will also trip out.A This results in a station outage for a time suicient to reclose all of the breakers and put the station back in operation. The result of such a prolonged outage is overspeeding of the generators and great accentuation of the system disturbance.

The earlier saturation excitation circuits sometimes stop igniting at a Voltage of the order of 90% of normal voltage while some of the latter design circuits will maintain operation down to 80% of normal line voltage. I propose to eliminate the serious consequences of a drop in line voltage in conjunction with ignitron stations excited from the high line voltage by the use of a voltage relay responsive to the excitation Voltage to simultaneously trip out the excitation voltage supply to all of the reactor firing circuits at some voltage above the failure point of the reactor system.

The simultaneous cutting out of all of the excitation systems permits immecliate reclosing of the contactors of the excitation systems on restoration of line voltage and thus prevents the necessity of opening and closing the main breakers to restore the station to operation. The use of the Voltage relay to control the excitation will, in general, limit the outage time to the length of time that the system fault actually exists, in general, too short `a time to permit great overspeeding Oi the generators supplying the load.

It is, accordingly, an object of my invention to provide a control system for simultaneously deenergizing the excitation circuits of all the cona'claims. (o1. ait-1m) 2, verters of a paralleloperating'conversion system in response to a predetermined drop in excitation potential'.

Itis a further objectv of my invention to provide an excitationsystem for reducingthe outage time caused by systemV disturbances.

Other objectsand advantages of my invention will bev apparent from the following description takenv in conjunction with the `accompanying drawing, in which:

Figure 1 is a schematic illustrationofa vaporelectric conversion system embodying my invention; and

Fig. 2 is a schematic illustration of a single unit of the system showing the details of the unit connections.

In the illustrative embodiment of my invention, an alternating-current circuit I0 is connected to a, direct-current circuit Il by meansv of a :plurality of vapor-electric devices A, B operating in parallel. For simplicity of illustration only two units are shown, butin normal installations' a greatl many units are so connected. Each unit A, Bl of'the device comprises a converter rtransformer I 2 connected to the alternating-current circuit I0 by a circuit breaker 52 and to a directcurrent circuit II by a circuit breaker 12, the flow of current between the circuits I'Il and II being controlled by a plurality of vapor-electric valves I3 herein illustrated' as of the make-alive type, in which each valve I3 comprises a main anode Il and cathode I5 and has an excitation electrode I6 in contact with the cathode I5.

An impulsing circuit 20 is provided for periodically applying excitation impulses to the make- -alive electrodes I5. The impulsing circuit 20 preferably is of the so-called reactor firing type in which a capacitor 2I is charged to a ring potential from any suitable source, herein illustrated as the high line I0, and the capacitor 2I is discharged by means of a non-linear reactor 2i preferably of the saturable reactor type.

For simplicity of illustration only two units of this system have been illustrated, but it will be understood that, in general, many units will be operated in parallel as certain operations such as that of electric chemical work frequently require power of the order of 200,000 kilowatts. In the event of a system fault producing a decrease in the high line voltage, the potential applied to the firing circuits 20 will likewise decrease, and at some point the firing circuits 20 will begin to fail to excite their associated converters.

To prevent this random occurrence I provide circuit breakers 3| between the source of excitamy invention, the breakers 52 and 'I2 will be l closed after which the master relay 30 will be energized by closing the series switch 28, placing the system in operation. The operation then will continue as long as the high line voltage remains normal. However, should any disturbance cause a reduction in the high line voltage, the excitation potential will be decreased so that the voltage relay 29 will open its contacts, deenergizing the .master control relay 30 which willsimultaneously open the circuits to all of the impulsing circuits 28 so that all of the converters A, B comprising the system will be simultaneously shut down without opening either the breakers 52 or 12. As-soon as the system disturbance has ceased, and the voltage has returned to normal, the voltage relay 29 will energize the master control relay 30 which simultaneously energizes all of the excitation circuits 2|J and restores the station to normal operation with the minimum of actuation time.

While for purposes of illustration I have described the specific embodiment of my invention, it will be apparent that changes and modifications rnay be made therein without departing from the true spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. An electric current translating system interconnecting two dissimilar electric circuits comprising a plurality of parallel operating converters, each of said converters including a plurality of vapor-electric valves of the make-alive type, a make-alive electrode for each of said valves, a wave distorting network for each of said converters for periodically applying impulses to the make-alive electrode of the valves thereof, a source of control potential, circuit means connecting said source to each of said wave distorting networks, circuit breaker means in each of said circuit means, and a relay responsive to the potential of said source of control potential for controlling said circuit breaker means for simultaneously controlling each of said circuit means.

2. An. electric current conversion system for transferring electric power between two dissimilar circuits, one of which is an alternating current circuit comprising a plurality of parallel operating valve type converters, a wave distorting network associated with each converter for supplying control impulses thereto, said wave distorting networks being unreliable when insucient potential is applied thereto, a source of control potential, connections from said source to said wave distorting networks, a voltage responsive relay energized from said source, circuit breaker means for controlling the connections from said source to all of said Wave distorting networks, and means energized by said voltage responsive relay for simultaneously actuating said circuit breaker means.

JOSEPH H. COX.

REFERENCES CITED The following references are of record in the ile of this patent:

UNITED STATES PATENTS 

